The streets of Shibam bustle with activity after Friday afternoon prayers. Founded on the Empty Quarter's southern edge in ancient times, the town once welcomed frankincense traders traveling Arabia's spice route. Today the Yemeni town still attracts desert traders but also intrepid tourists, who come to see the distinctive mud-brick skyscrapers that house the town's 5,000 residents. Usually between four and eight stories high, the structures have earned Shibam a nickname: "the Manhattan of the Desert." See an aerial video of the city.